The present invention relates broadly to a radar calibration apparatus, and in particular to a calibration apparatus utilizing direct measurement equipment in conjunction with oblique photometry.
The recent emergence of single aircraft active and passive sensor systems with highly directive arrays have identified the need for accurate calibration of the sensor angle indicators and range indicator (for active systems) devices. A number of calibration schemes for for sensors are presently in use but most of procedures are limited since they violate one or more fundamentals which are basic to calibration. A system undergoing calibration should use an independent measurement scheme in order to determine if bias errors are present. Additionally, the calibration measurement system must be compared to a standard, and the calibration process must be dynamic with observations in the direction that the sensor is pointing and in the environment that the sensor is to operate.
Radar using precision ranging and monopulse tracking can locate ground targets in geodetic coordinates. Large RF bandwidth and large phased arrays make possible range measurements with standard errors of a few feet and standard error in directivity of a fraction of a milliradian. Inertial equipment in the aircraft on which the radar is mounted and gyros mounted on the radar antenna provide accurate antenna coordinate orientation in inertial space. Monopulse technique provides continuous track of ground targets and provides accurate angle error information. Angle error is continuously adjusted to zero by altering phase of antenna elements in the radar array, maintaining continuous track of the ground target. Angle indicator provides measurement of the direction to the target or terrain features with respect to the local coordinate system.